Issue 47842. Add a test for extension from other package.

Bug: https://github.com/dart-lang/sdk/issues/47842
Change-Id: Ib6c4d6791f823191ef39998a6e350c48915d52fa
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/222243
Reviewed-by: Phil Quitslund <pquitslund@google.com>

pkg/analysis_server/test/src/services/correction/fix/fix_processor.dart

@@ -264,8 +264,7 @@ abstract class FixProcessorTest extends BaseFixProcessorTest {
 
   Future<void> addUnimportedFile(String filePath, String content) async {
     addSource(filePath, content);
-    var result = await session.getResolvedUnit(convertPath(filePath));
-    extensionCache.cacheFromResult(result as ResolvedUnitResult);
+    await cacheExtensionsForFile(filePath);
   }
 
   Future<void> assertHasFix(String expected,
@@ -378,6 +377,11 @@ abstract class FixProcessorTest extends BaseFixProcessorTest {
     await _assertNoFixAllFix(error);
   }
 
+  Future<void> cacheExtensionsForFile(String path) async {
+    var result = await session.getResolvedUnit(convertPath(path));
+    extensionCache.cacheFromResult(result as ResolvedUnitResult);
+  }
+
   List<LinkedEditSuggestion> expectedSuggestions(
       LinkedEditSuggestionKind kind, List<String> values) {
     return values.map((value) {

pkg/analysis_server/test/src/services/correction/fix/import_library_project_test.dart

@@ -234,6 +234,48 @@ void f(String s) {
 ''');
   }
 
+  @FailingTest(reason: 'We suggest importing src/b.dart')
+  Future<void> test_extension_otherPackage_exported_fromSrc() async {
+    var pkgRootPath = '/.pub-cache/aaa';
+
+    var a = newFile('$pkgRootPath/lib/a.dart', content: r'''
+export 'src/b.dart';
+''');
+
+    var b = newFile('$pkgRootPath/lib/src/b.dart', content: r'''
+extension IntExtension on int {
+  int get foo => 0;
+}
+''');
+
+    writeTestPackageConfig(
+      config: PackageConfigFileBuilder()
+        ..add(name: 'aaa', rootPath: pkgRootPath),
+    );
+
+    updateTestPubspecFile('''
+dependencies:
+  aaa: any
+''');
+
+    await cacheExtensionsForFile(a.path);
+    await cacheExtensionsForFile(b.path);
+
+    await resolveTestCode('''
+void f() {
+  0.foo;
+}
+''');
+
+    await assertHasFix('''
+import 'package:aaa/a.dart';
+
+void f() {
+  0.foo;
+}
+''');
+  }
+
   Future<void> test_invalidUri_interpolation() async {
     addSource('$testPackageLibPath/lib.dart', r'''
 class Test {